This invention relates to apparatus and method for inhibiting the hardening of concrete in a concrete mixer and, in one aspect, for protecting concrete mixer trucks from becoming bound up with a hardened charge of concrete, e.g., such as when such trucks become disabled in the field.
Concrete batch fabrication plants, commonly termed "ready-mix" plants, are widely in service today throughout the country for preparing concrete mixes consisting of water, cement, and aggregates of various sizes. Freshly batched concrete mixes are dispensed from such plants into concrete mixer trucks each having a revolving drum, and trucks filled with a charge of concrete mix transport the concrete to one or more job sites for pouring. After delivery of the concrete mix, the trucks return to the ready-mix plant for a new charge of concrete mix for delivery to the next job site. At the end of each day, the trucks are finally washed out to remove the accumulated deposits within the rotatable mixing drum.
As is pointed out in Black et al U.S. Pat. No. 4,226,542, the concrete mix remaining in a truck returning to the ready-mix plant for many years was simply dumped in the yard and allowed to harden. Eventually, the hardened concrete could be hauled away for use as landfill. However, the dumping of returned concrete at the ready-mix plant was found to be environmentally unsound, and attempts have been made to reclaim portions of the returned concrete mix to provide less environmentally damaging operations. U.S. Pat. No. 4,226,542 is one such attempt at reclaiming unused concrete mix returned to the ready-mix plant by removing aggregates from the concrete mix with a screw classifier. Returned concrete mix is dumped into an inlet hopper having a screw classifier for removing aggregate and coarse sand, and a weired channel enables gravity flow of the water, cement fines, and sand fines constituents into a slurry vessel.
Concrete construction operations today are performed almost entirely by delivering wetted premixed concrete for on-site pouring from ready-mix plants as described above. The wetted premixed concrete comprises wetted cement in the concrete mixer of delivery trucks, and this wetted cement will chemically bind with the water and thereby set up or harden in a certain amount of time. A significant problem develops when one of these delivery trucks filled with a charge of wetted concrete premium breaks down or otherwise is delayed in reaching a location where the wetted concrete can be dumped without adverse environmental impact. The problem arises when the concrete sets up or hardens in the rotatable drum of the delivery truck. The hardened concrete then must be removed with much difficulty from the rotatable drum by picks or jackhammers or the like. Oftentimes, it is impossible to remove the hardened concrete without destroying the integrity of the rotatable concrete mixer drum on the delivery truck.
It is an object of the present invention to provide apparatus and method for protecting the integrity of concrete mixers containing wetted concrete premix.
It is a further object of the present invention to provide a concrete mixer and method capable of inhibiting the hardening of a wetted concrete premium in those circumstances when the wetted concrete cannot be unloaded from the concrete mixer.
It is yet another object of the present invention to protect concrete mixer trucks from becoming bound up with a hardened concrete in an emergency circumstance when becoming disabled in the field.
These and other objects of the present invention will become apparent from the detailed description as follows.